The orange wheat blossom midge, Sitodiplosis mosellana (SM) (Diptera: Cecidomyiidae), is found around the world wherever wheat is grown. Larvae feed on developing kernels, causing them to shrivel, crack, and deform (1). Grain yield decreases exponentially with the increase in SM larval infestations (2). Damaged kernels are inferior in milling quality and germination capacity (1). SM larval infestations are also correlated with the presence of wheat scab, Fusarium graminearum, and glume blotch, Septoria nordorum (Berk.), suggesting that SM adults vector fungal spores (3).
Several outbreaks of the SM have been reported in North America since this pest insect became established in Quebec in 1828. In recent years, significant damage to wheat crops occurred in Saskatchewan, Manitoba, Alberta, North Dakota, and Minnesota. In 1983, for example, SM reached epidemic populations in northeastern Saskatchewan, causing revenue losses of &gt;$ 30 million (2). Since then, SM populations have spread across the Northern Plains including most of the wheat-growing area. In 1995, yield losses in Saskatchewan reached 30% in many fields and averaged 15% in the Red River Valley of North Dakota and Minnesota (4). In the same year, total losses exceeded $ 50 million in Manitoba and $ 100 million in Saskatchewan. In North Dakota in 1995, wheat producers lost an estimated 7 million bushels in wheat yield, and $ 30 million in gross revenue due to SM (5).
Cultural, biological and chemical control tactics are employed to manage SM populations. Cultural practices include crop rotation to non-preferred crops, seeding early or late (6), and selecting early maturing varieties. Wheat cultivars resistant to SM would result in long-term reduction of damage (7, 8), but are not yet available. Various biological control agents, such as spiders, mites and hymenopterous parasitoids, prey upon SM populations, but significant crop damage still occurs (9, 10). Insecticides are the current means of controlling SM populations. A single, well-timed application of an insecticide suppresses SM populations, improving crop yield and increasing the farmers' profit (11, 12).
Monitoring of wheat fields is required to identify SM infestations and to take appropriate control measures. Current assessments of SM populations are time-consuming, tedious and not user-friendly. These tactics include captures of adult SM in colored traps, and recording numbers of SM eggs, larvae or adults on heads of wheat (13, 14, 15). Colored traps afford many by-catches which are not readily distinguished from SM. Counts of eggs are laborious and require the use of a stereomicroscope. Counts of adult SM on wheat heads are confounded by the presence of "midge look-a-likes". Uncertain about their SM population assessment, wheat producers often decide to apply unnecessary and costly "insurance sprays". Moreover, ill-timed insecticide applications are not cost-effective, environmentally unacceptable, and adversely affect biological control agents.
Between 1992-3, evidence was presented that female SM produce a sex pheromone to attract male SM (16, 17). This document describes the identification, synthesis and field testing of the SM pheromone.